You are right, there is not much documentation on the parameters passed into OOTB UI javascript extension points. As you mentioned, stopping the execution or doing something like console.log(scope) in the only way. Wondering if you looked at the Alfresco Application Development Framework (ADF) which is the recommended approach if you really want to do additional client side logic and customization? Here are some helpful links on ADF:

With the next release (1.8) of APS due next week, there will be a production grade ADF based UI made available as part of APS s/w. Most of the runtime features which are now available in OOTB UI, will be available in this app too. As a customer you can get full access to the source of this app to customize and make it your own! The ADF equivalent of those javascript extension points can be found in https://alfresco.github.io/adf-component-catalog/injectables/FormService.html#readme